fix(router): Use official javascript content type

application/x-javascript is obsolete and shouldn't be used. http://stackoverflow.com/a/9664327
feat(router): Improved router defaults

Use recommended values from
https://github.com/h5bp/server-configs-nginx/blob/master/nginx.conf
Merge pull request #2040 from johanneswuerbach/patch-6

fix(router): Use official javascript content type